Numerous expandable endoluminal prostheses are known in the art which are adapted for temporary or permanent implantation within a body lumen for maintaining the patency of the lumen. Examples of lumens, both native and artificially made, in which endoluminal prostheses may be implanted include, without limitation: arteries, such as those located within the coronary, mesentery, peripheral, or cerebral vasculature; veins; gastrointestinal tract; biliary tract; urethra; trachea; hepatic shunts; and fallopian tubes.
Each of the various types of endoluminal prostheses known in the art provides a uniquely beneficial structure to modify the mechanics of the targeted luminal wall. Many devices known in the art are also designed to provide a desirable healing surface for the vessel wall following treatment. Others are designed to achieve further objectives such as, for example, excluding an aneurysm.
For example, devices generally referred to as stents provide radial support to the lumen. Stents may be mechanically expandable, balloon expandable or self-expanding. Stent-grafts are typically stents with a covering, lining, coating, or some combination of the foregoing. Various grafts, stents, and combination stent-graft prostheses have been previously disclosed for implantation within body lumens.
A common procedure to enlarge a stenotic or diseased blood vessel is known as percutaneous transluminal angioplasty, or PTA. PTA employs an angioplasty balloon catheter which is inserted at a site remote from the site of treatment, tracked to the stenosis, and placed across the lesion. The balloon is then inflated to dilate the artery. In order to prolong the positive effects of PTA and to provide long-term radial support to the treated vessel, a stent or stent-graft may be implanted in conjunction with the procedure. Under this procedure, the stent may be mounted on the balloon, collapsed to an insertion diameter, delivered to the treatment site within the affected lumen, and deployed to its desired diameter for treatment. Because the procedure requires insertion of the stent at a site remote from the site of treatment, the device must be guided through the potentially tortuous conduit of the body lumen to the treatment site. Therefore, the stent must be capable of being reduced to a small insertion diameter and must be flexible.
During an angioplasty procedure, atheromatous plaques within the vessel can undergo fissuring, thereby creating a thrombogenic environment in the lumen. Excessive scarring may also occur following the procedure, potentially resulting in restentosis or reocclusion of the treated lumen. Attempts to address these problems include providing a suitable surface within the lumen for more controlled healing to occur in addition to the support provided by a stent. These attempts include providing a lining or covering in conjunction with an implanted stent. A stent with such a lining or covering is known in the art as a stent-graft.
Specific examples of stents include U.S. Pat. Nos. 5,292,331 and 5,674,278, both issued to Boneau, which are herein incorporated by reference. The stent of Boneau comprises a, or a series of sinusoidally shaped ring-like. Such a stent exhibits excellent radial strength and flexibility.
Other types of stents are disclosed in U.S. Pat. Nos. 4,733,665, 4,776,337, 4,739,762 and 5,102,417 all issued to Palmaz, U.S. Pat. No. 5,195,984 issued to Schatz, U.S. Pat. No. 5,421,955 issued to Lau et al., or U.S. Pat. No. 5,449,373 issued to Pinchasik et al. Such stents include examples of stents created by removing material, such as by cutting or forming, from a thin-walled tube or sheet of material.
All of the foregoing examples of stents may be used alone or in conjunction with a graft. The graft component, or membrane, of a stent-graft may prevent excessive tissue prolapse or protrusion of tissue growth through the interstices of the stent while allowing limited tissue in-growth to occur to enhance the implantation. The surface of the graft material at the same time may minimize thrombosis, prevent scarring from occluding the lumen, prevent embolic events and minimize the contact between the fissured plaque and the hematological elements in the bloodstream.
A combination stent-graft may serve other objectives, such as delivering therapeutic agents via the assembly, excluding aneurysms or other malformations, occluding a side branch of a lumen without sacrificing perforator branches, conferring radiopacity on the device, and others. Various designs to achieve these objectives include stents partially or completely coated or covered with materials, some of which are impregnated with therapeutic agents, radiopaque elements, or other features designed to achieve the particular objectives of the device.
Various methods of manufacturing graft devices alone have been disclosed in the art. One such method for manufacturing a graft is disclosed in U.S. Pat. No. 5,641,373, issued to Shannon et al. The disclosed method comprises reinforcing an extruded fluoropolymer tube with a second fluoropolymer tube. The second tube is prepared by winding fluoropolymer tape around the exterior of a mandrel and heating it to form a tube. The graft may then be mounted on an anchoring mechanism such as a stent or other fixation device.
Another example of a graft is disclosed in U.S. Pat. No. 4,731,073, issued to Robinson. The graft disclosed therein comprises multiple layers of segmented polyether-polyurethane which form multiple zones having varying porosities.
U.S. Pat. No. 5,628,786, issued to Banas, discloses a polytetrafluoroethylene (PTFE) graft which has a reinforcing structure integrally bound to the graft. The reinforcing structure may be in the form of a rib which is sintered or otherwise integrally bound to the graft.
U.S. Pat. No. 5,207,960, issued to Moret de Rocheprise, discloses a process for the manufacture of a thin-walled tube of fluorinated resin tape. The method includes winding the tape around a mandrel and sintering the tape. While still on the mandrel, the tube is rolled to elongate the tube, to reduce the thickness of the tube, and to facilitate removal of the tube from the mandrel. The patent discloses that the tubes obtained can be used particularly as sheaths for the lining of metal tubes.
There are also numerous examples of combination stent-grafts disclosed in the art. U.S. Pat. No. 5,667,523 issued to Bynon et al. discloses a stent-graft comprising two stents and graft material positioned between the two stents.
U.S. Pat. No. 5,653,747 issued to Dereume discloses a stent to which a graft is attached. The graft component is produced by extruding polymer in solution into fibers from a spinnerette onto a rotating mandrel. A stent may be placed over the fibers while on the mandrel and then an additional layer of fibers spun onto the stent. The layer or layers of fibers may be bonded to the stent and/or one another by heat or by adhesives.
PCT Application WO 95/05132 discloses a stent around which a thin film of PTFE has been wrapped circumferentially one time and overlapped upon itself to form a seam. The stent may be alternatively or additionally placed to cover the interior of the stent. Fluorinated ethylene propylene is used as an adhesive to affix the graft to the stent.
An example of a stent and tubular graft is disclosed in U.S. Pat. No. 5,522,882 issued to Gaterud, et al. Gaterud discloses an expandable stent mounted on a balloon and a graft mounted over the stent.
U.S. Pat. No. 5,123,917 issued to Lee discusses a flexible and expandable inner tube upon which separate ring-like scaffold members are mounted, and a flexible and expandable outer tube enclosing the inner tube and scaffold members. The rings may be secured to the inner liner with an adhesive layer. Alternatively, the liners may be adhered to each other with the rings trapped between the layers. Lee discloses that the luminal surface of the device may be coated with various pharmacological agents.
Similarly, U.S. Pat. Nos. 5,282,823 and 5,443,496, both issued to Schwartz, et al. disclose a stent with a polymeric film extending between the stent elements, and strain relief means in the form of cuts in the film to allow the stent to fully expand and conform to the interior of the lumen. The thin polymeric film is applied to the stent while in solution and dried. Once dried, cuts are made in the film to provide strain relief means.
Another assembly includes a stent embedded in a plastic sleeve or stitched or glued to a nylon sleeve, as in U.S. Pat. No. 5,507,771, issued to Gianturco. Other references disclosing devices in which the graft is stitched to the stent include European Patent Application EP 0 686 379 A2, which teaches a perforate tubular frame having a fabric liner stitched to the frame, and World Intellectual Property Organization Application Number WO 96/21404 which indicates that the graft be stitched to the stent, and possibly to loops or eyelets which are part of the stent structure.
U.S. Pat. No. 5,637,113 issued to Tartaglia teaches a stent with a sheet of polymeric film wrapped around the exterior. Tartaglia teaches that the film is attached to the stent at one end by an adhesive, by a hook and notch arrangement, or by dry heat sealing. The polymer can also be attached to the stent by wrapping the film circumferentially around the stent and attaching the polymer film to itself to form a sleeve around the stent by heating and melting the film to itself, adhesive bonding, solvent bonding, or by mechanical fastening, such as by a clip. The film may be loaded or coated with a therapeutic agent.
U.S. Pat. No. 5,628,788, issued to Pinchuk, discloses a process of melt-attaching a graft to a stent by disposing a layer of material between the stent and graft which has a lower melting point than the graft, and heating the assembly to the melting point of the low-melting point material. Pinchuk also teaches adhering a textile graft to a stent by coating a stent with vulcanizing silicone rubber adhesive and curing the adhesive. Pinchuk discloses a similar stent-graft assembly in European Patent Application EP 0 689 805 A2 and teaches that the graft member can be bonded to the stent member thermally or by the use of adhesive agents.
Similarly, World Intellectual Property Organization Application No. WO 95/05132 discloses a stent with an inner and/or an outer liner wrapped around the stent to form a seam, with the liner(s) affixed using an adhesive or melt-attached using a layer of a material with a lower melting point.
U.S. Pat. No. 5,645,559, issued to Hachtman, et al., discloses a multiple layer stent-graft assembly comprising a first layer defining a hollow tubular construction, a second layer having a self-expanding braided mesh construction and a layer of polymeric material disposed between the first and second layers. The polymeric material may be adhered by two-sided adhesive tape. The self-expanding braided mesh, the tubular material, or both may be larger in diameter in the distal regions than in the medial region.
U.S. Pat. No. 5,534,287, issued to Lukic, discloses methods which result in a covered stent, the covering adhered via a lifting medium.
U.S. Pat. No. 5,674,241, issued to Bley, et al. teaches that a hydrophilic polymer layer may be laminated, embedded, coated, extruded, incorporated, or molded around an expandable mesh stent while the stent is in its collapsed condition, and the stent and graft permitted to expand upon hydration.
European Patent Application No. EP 0 775 472 A2 discloses a PTFE-covered stent. The stent can be covered by diagonally winding an expanded PTFE tape under tension around an at least partially expanded stent.
Challenges arising in the art which none of the prior art adequately addresses include achieving an optimal stent-graft design for delivery and deployment of the device. Other challenges which are not adequately addressed by the prior art include minimizing, if not eliminating, migration of the stent, graft or stent-graft; and minimizing thrombogenic potential, vessel reocclusion and tissue prolapse following deployment. Shortcomings associated with the prior art include: assemblies with undesirably large crossing profiles; assemblies with insufficient flexibility; inadequate adhering of coatings and coverings to stents; failure to shield the injured vascular surface; failure to prevent tissue ingrowth from occluding the lumen; failure to minimize the embolization of particles loosely adherent to the vessel wall (especially during device placement and deployment); and increased thrombogenic potential arising from flaps formed in the graft material.